In the process for manufacturing the herbicide barban it is desirable to avoid use of 4-chloro-2-butyn-1-ol as a reagent. Therefore, as disclosed in U.S. Pat. No. 3,155,713 a preferable manufacturing procedure employs as a final step the substitution of chlorine for the hydroxy group of 4-hydroxy-2-butynyl N-(3-chlorophenyl) carbamate. The use of thionyl chloride as chlorinating reagent is disclosed in the patent. U.S. Pat. No. 3,226,426 discloses use of thionyl chloride in combination with pyridine to give an 83.6 percent yield of crude reaction product. Although this method admittedly is not free from side reactions and the product contains various impurities, still overall results are better than are obtained with other reagent systems which are available for replacement of hydroxy groups with chlorine. The presence of carbamate structure in the molecule, which may react with chlorinating agents, presents a difficult problem and severely limits the choice of reagent systems.
In the chlorination of a simple acetylenic alcohol, as for example, 2-butyne-1,4-diol, a much simpler situation exists with respect to possible side reactions, so that a greater variety of chlorinating reagents may be used, including reagents which are more effective. Yields of better than 90 percent have been disclosed in German Pat. Nos. 1,133,716 and 1,135,893 in reaction of butynediol and propargyl alcohol with the reagent system consisting of thionyl chloride or phosgene in combination with dimethylformamide. This reagent system is unique in some respects. It is known, for example, that dimethylformamide and thionyl chloride form an adduct which can be isolated (M. D. Scott and H. Spedding, J. Chem. Soc. 1968 p. 1603-1609). I have discovered that this very active reagent system may be used to replace the hydroxy group on 4-hydroxy-2-butynyl m-chlorocarbanilate in better yields and with less formation of by-products than the more gentle reagent systems which have been employed in the past.